Screening device



Sept. 15, 1964 M. M. CANNON ETAL SCREENING DEVICE 2 Sheets-Sheet 1 Original Filed May 5, 1959 Sept. 15, 19 4 M. M. CANNON ETAL SCREENING DEVICE 2 Sheets-Sheet 2 Original Filed May 5, 1959 United States Patent 3,149,067 SCREENING DEVICE Madison Mott Cannon, Weilesley, Mass., George McKinstry Dick, Sherbrooke, Quebec, Canada, and Salomon Maury Salomon, Madison, Wis, assignors to Bird Machine Company, South Walpole, Mass, a corporation of Massachusetts Continuation of application Ser. No. 811,136, May 5, 1959. This application Aug. 23, 1962, Ser. No. 219,818 3 Claims. (Cl. 209273) This invention relates to a device for screening liquid suspensions of solid particles and pertains more specifically to a device for screening aqueous paper pulp suspensions to remove undesired particles of dirt or the like from the suspension.

Although a variety of devices have been proposed embodying cylindrical screens for screening liquid suspensions by the flow of the suspension outwardly through the screen, such devices have not been completely effective in separating the dirt and other undesired particles from the suspension. I have now discovered that the effectiveness of such cylindrical screen devices can be improved by proper control of the flow pattern of the suspension in the proximity of the screen.

One object of the present invention is to provide a device for screening liquid suspensions embodying a cylindrical screen together with means for controlling the flow pattern of the suspension immediately in advance of its passage outwardly through the screen by confining the suspension to a generally annular chamber or passageway having a width which is only a small fraction of the diameter of the screen.

Another object is to provide a device of the character described in which means is provided for introducing a uniformly thin stream of liquid suspension tangentially to the inner face of the cylindrical screen at one end thereof and for passing the stream spirally through an annular chamber across the inner face to the opposite end of the screen.

Other and further objects will be apparent from the drawing and from the description which follows.

In the drawing:

FIG. 1 is a view in side elevation, partly broken away and in section, showing one embodiment of the present invention;

FIG. 2 is a view in horizontal section taken along line 22 of FIG. 1; and

FIG. 3 is a view in horizontal section, partly broken away, showing another embodiment of the invention.

In the embodiment shown in the drawing, the device comprises a main frame 15) in which is mounted an annular chamber having a fixed smooth imperforate inner wall 12 and a fixed outer wall 14. Supported within the hollow central portion of the chamber is a pair of bearings 16, 18, these hearings being mounted on annular support plates 17, 19 which are in turn bolted to annular bosses 21, 21 integral with inner wall 12. Bearings 16, 18 serve to carry a drive shaft 20 fixed to the lower end of which is a multiple V-beit drive sheave 22 driven from any suitable source of power such as an electric motor (not shown) by means of V-belts 24.

Mounted within the annular chamber defined by inner and outer walls 12, 14 is a fixed cylindrical screen plate 26 supported by a grid of spaced ribs 28, 28, the grid being in turn supported at top and bottom by outer wall 14 and both inner Wall 12 and outer wall 14 being substantially coextensive in length with screen 26. An annular inlet chamber 30 is provided at the upper end of the device including inlet 32 through which a supply of the liquid suspension is introduced, the inlet chamber serving to provide a stream of liquid suspension which is directed tangentially of the inner face of screen 26 along its upper periphery, the stream of suspension passing downwardly into the annular passageway between screen 26 and inner wall 12.

The space between screen 26 and outer wall 14 serves as a receiving chamber for receiving the acceptable suspension passing through screen 26, this chamber being sealed at top and bottom so that any suspension entering the chamber must pass through screen 26. The accepted material flows outwardly through main delivery outlet 34, while that portion of the liquid suspension containing the rejected particles flows outwardly through reject outlet 36 which extends tangentially from the bottom or outlet end of the annular passageway between screen 26 and inner wall 12, outlet 36 extending in the same sense as the direction of travel of the stream of liquid suspension which is introduced through inlet 32, as best appears in FIG. 2.

In order to prevent plugging or obstruction of the screen, a pair of foils 38, 40 of any suitable construction is mounted on a pair of supporting rings 42, 42 and hung from supporting arms 44, 44 secured to the upper end of shaft 20. Foils 38, 40 extend downwardly into the annular passageway between inner wall 12 and screen 26 in a position closely adjacent to the inner face of screen 26 and serve to clear the face of the screen as they move past it driven by rotation of shaft 20.

While both screen 26 and inner wall 12 may be in the form of concentric cylinders to provide an annular passageway of perfectly uniform dimensions throughout its periphery, it is preferred, as shown in FIG. 1, to make the surface of wall 12 slightly conical so that the width of the annular passageway between the wall and the screen is slightly greater at the upper or inlet end of the screen than at the lower or outlet end. This gradual diminution of spacing between the screen and the opposing inner wall serves to compensate at least in part for the diminution in volume of the liquid suspension proceeding from the inlet toward the outlet end which is occasioned by the passage of a portion of the suspension through the screen.

It is highly important that the spacing between the smooth imperforate inner Wall 12 and the coaxial cylindrical screen 26 be kept as small as possible while still permitting free rotation of foils 38, 40. In general, the spacing between inner wall 12 and screen 26 should be from 2% to 20% of the diameter of the screen with the percentage decreasing as the diameter of the screen increases. For example, with small screens having a diameter of 18 inches, the spacing should be no more than three inches, while with large screens such as those having a diameter of 60 inches, the spacing should be no more than five inches.

The close spacing between inner wall 12 and screen 26 minimizes backfiow of the dispersion and tends to prevent fresh dispersion entering the passageway from becoming mixed with a portion of the dispersion which has already been subjected to screening action. More uniform screening action and more reliable performance are thus promoted. Inner wall 12, having a smooth imperforate surface and being of circular cross-sectional configuration throughout, serves to maintain the stream of suspension in the form of a relatively thin layer closely adjacent the inner face of screen 26 as it passes spirally toward the outlet end and provides for a smooth, uniform flow of the suspension across and through the screen with a minimum of interference and of turbulence.

Furthermore, reject outlet 36, extending tangentially outwardly from the lower end of the passageway between inner wall 12 and screen 26, facilitates separation and complete removal of oversized and dirt particles which are rejected by the screen, taking advantage of the fact that these panticles are usually of higher specific gravity than the acceptable particles of the suspension and hence tend to be driven outwardly by their momentum as they are carried in spiral path toward the reject outlet. In another embodiment, as shown in FIG. 3, the reject outlet 50 extends radially outwardly from the annular passageway between inner wall 12 and screen 26. This construction also takes advantage of the high specific gravity of the dirt particles and their consequent tendency to be thrown outwardly from the passageway.

The foils 38, 40 are preferably rotated in a clockwise direction as seen in FIG. 2 so that they rotate in the same sense as the suspension introduced tangentially through inlet 32. It is also possible, however, to reverse the direction of rotation of the foils so that they move in a direction counter to the flow of liquid suspension with satisfactory results.

This application is -a continuation of application Serial No. 811,136. filed May 5, 1959, and now abandoned.

Although specific embodiments of the invention have been described herein, it is not intended to limit the invention solely thereto, but to include all of the obvious variations and modifications within the spirit and scope of the appended claims.

What is claimed is:

1. A device for separating aqueous suspensions containing particles of solid material into a stream of acceptable suspension and a stream of rejected suspension which comprises a vertically disposed housing, a fixed cylindrical screen vertically disposed within and spaced from the inner wall of said housing, a fixed, imperforate, generally cylindrical wall member of circular cross-sectional configuration coextensive in length with said screen mounted concentrically within and spaced from the screen by a distance equal to 2% to 20% of the diameter of the screen and no greater than 3 inches for a screen 18 inches in di ameter and no greater than 5 inches fora screen 60 inches in diameter to form an annular passageway, means for introducing a stream of liquid suspension to be separated at one end of said passageway, means for withdrawing rejected suspension from the other end of said passageway, means disposed radially outwardly of said screen for receiving accepted suspension after its passage through the screen, and means extending into said passageway for clearing the inlet face of the screen, said means for introducing the stream of liquid suspension to be separated comprising an inlet for introducing said stream tangentially to said housing whereby the liquid suspension flows into the spam between said screen and said housing to said annular passageway and said means for withdrawing the rejected suspension comprising an outlet extending tangentially outwardly from said passageway in the same sense as the direction of travel of said stream in liquid suspension.

2. A device as defined in claim 1 in which the spacing between said screen and said wall member diminishes gradually from the inlet end to the outlet end thereof.

3. A device for separating aqueous suspensions containing particles of solid material into a stream of acceptable suspension and a stream of rejected suspension which comprises a vertically disposed housing, a fixed cylindrical screen vertically disposed within and spaced from the inner Wall of said housing, a fixed, imperforate, generally cylindrical wall member of circular cross-sectional configuration coextensive in length with said screen mounted concentrically within and spaced from the screen by a distance equal to 2% to 20% of the diameter of the screen and no greater than 3 inches for a screen 18 inches in diameter and no greater than 5 inches for a screen inches in diameter to form an annular passageway, means for introducing a stream of liquid suspension to be separated at one end of said passageway, means for withdrawing rejected suspension from the other end of said passageway, means disposed radially outwardly of said screen for receiving accepted suspension after its passage through the screen, and means extending into said passageway for clearing the inlet face of the screen, said means for introducing the stream of liquid suspension to be separated comprising an inlet for introducing said stream tangentially to said housing whereby the liquid suspension flows into the space between said screen and said housing to said annular passageway and said means for Withdrawing the rejected suspension comprising an outlet extending outwardly from said passageway.

References Cited in the file of this patent UNITED STATES PATENTS 1,696,354 I-Iaug Dec. 25, 1928 2,835,173 Martindale May 20, 1958 2,902,156 Dahlberg Sept. 1, 1959 

1. A DEVICE FOR SEPARATING AQUEOUS SUSPENSIONS CONTAINING PARTICLES OF SOLID MATERIAL INTO A STREAM OF ACCEPTABLE SUSPENSION AND A STREAM OF REJECTED SUSPENSIONS WHICH COMPRISES A VERTICALLY DISPOSED HOUSING, A FIXED CYLINDRICAL SCREEN VERTICALLY DISPOSED WITHIN AND SPACED FROM THE INNER WALL OF SAID HOUSING, A FIXED, IMPERFORATE, GENERALLY CYLINDRICAL WALL MEMBER OF CIRCULAR CROSS-SECTIONAL CONFIGURATION COEXTENSIVE IN LENGTH WITH SAID SCREEN MOUNTED CONCENTRICALLY WITHIN AND SPACED FROM THE SCREEN BY A DISTANCE EQUAL TO 2% TO 20% OF THE DIAMETER OF THE SCREEN AND NO GREATER THAN 3 INCHES FOR A SCREEN 18 INCHES IN DIAMETER AND NO GREATER THAN 5 INCHES FOR A SCREEN 60 INCHES IN DIAMETER TO FORM AN ANNULAR PASSAGEWAY, MEANS FOR INTRODUCING A STREAM OF LIQUID SUSPENSION TO BE SEPARATED AT ONE END OF SAID PASSAGEWAY, MEANS FOR WITHDRAWING REJECTED SUSPENSION FROM THE OTHER END OF SAID PASSAGEWAY, MEANS DISPOSED RADIALLY OUTWARDLY OF SAID SCREEN FOR RECEIVING ACCEPTED SUSPENSION AFTER ITS PASSAGE THROUGH THE SCREEN, AND MEANS EXTENDING INTO SAID PASSAGEWAY FOR CLEARING THE INLET FACE OF THE SCREEN, SAID MEANS FOR INTRODUCING THE STREAM OF LIQUID SUSPENSION TO BE SEPARATED COMPRISING AN INLET FOR INTRODUCING SAID STREAM TANGENTIALLY TO SAID HOUSING WHEREBY THE LIQUID SUSPENSION FLOWS INTO THE SPACE BETWEEN SAID SCREEN AND SAID HOUSING TO SAID ANNULAR PASSAGEWAY AND SAID MEANS FOR WITHDRAWING THE REJECTED SUSPENSION COMPRISING AN OUTLET EXTENDING TANGENTIALLY OUTWARDLY FROM SAID PASSAGEWAY IN THE SAME SENSE AS THE DIRECTION OF TRAVEL OF SAID STREAM IN LIQUID SUSPENSION. 